940
FXUS61 KPBZ 030006
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
806 PM EDT Wed Apr 2 2025

.SYNOPSIS...
Storms could be severe tonight into tomorrow. Multiple days of
rain will lead to river rises and localized flooding concerns. A
Flood Watch remains in effect for eastern Ohio.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:

- Another round of thunderstorms, possibly severe, overnight
  tonight with a squall line
- A Flood Watch is in effect for portions of eastern Ohio.
-------------------------------------------------------------------

A cluster of showers and isolated storms has dissolved this
evening with the exit of the warm front. Weak forcing within the
warm sector will keep convection low through midnight. With
strong warm advection from the southwest, expect temperatures to
rise slightly despite the loss of surface heating.

Showers and thunderstorms will move through overnight as a cold
front and shortwave trough approach from the west. Arrival of
the disturbance in eastern Ohio/northwest PA is projected for
midnight to 2am timeframe.

The potential for severe storms increases along a pre- frontal
trough with a squall line moving across Ohio with upscale growth
supported by paralleling deep layer southwesterly flow. Again
though, we look to be in a setup where the storms will move in
locally in an unfavorable diurnal timing window for surface-
based instability; HREF probability for >100 J/kg of SBCAPE
doesn`t exceed 20% in our area overnight with a warm nose
extending up to 850 mb. CAM point soundings suggest some more
MUCAPE (potentially up to 750 J/kg) available atop the low level
warm nose. Shear will not be an issue with a low level jet
maximum nearing 70 knots at 850 mb, and thus the 0-3 km shear
values are progged in excess of 40 knots with deep layer shear
nearing 60 knots. What this all means is that there`s again a
conditional probability, dependent on storms being surface
based, for damaging wind and an embedded tornado given the low
level shear parameters and veering in the lowest few km. The
segments of the line to pay close attention to would be those
oriented more northwest to southeast to best ingest the
available low level shear. Should the storms be elevated,
though, threats would likely be limited to small hail and heavy
rain. SPC has maintained the Slight Risk (2/5) west of I-79 and
a Marginal Risk (1/5) farther east.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
KEY MESSAGES:

- Showers and thunderstorms continue through the rest of the
  work week as a front stalls near the local area.
- Some storms could be severe on Thursday.
- A Flood Watch remains in effect for portions of eastern Ohio.
-------------------------------------------------------------------

The forward progress of the front is expected to slow and stall on
Thursday as the upper level flow establishes out of the southwest
and transports anomalously high (+3 to 4 standard deviations)
precipitable water into the region. Uncertainty in the exact
position of the front exists, which will impact areas where
convergence is strongest and heavy rain falls, and also which areas
have the potential for severe storms. At this time, the southern
half of the area (especially south of I-70) is favored for having a
more conducive environment for organized deep convection and severe
potential on Thursday, but there will likely be some wiggle room as
models still try to pin down the placement of the boundary. This
threat continues to be highlighted by SPC with a Slight Risk (2/5)
which has been pulled south of the Mason-Dixon Line while a Marginal
Risk (1/5) extends up to US-422. CAPE profiles look to be taking
on a taller and skinnier look with deep saturation and a
weakening low level wind field, so the severe threat may be
limited to small hail and gusty wind with heavy rain. HREF
probs are around 50-70% for another half an inch, but could be
locally higher in heavier thunderstorms.

The front is progged to drift south of the area late Thursday or
Thursday night, which will lead to a decrease in POPs from north to
south during that time as the primary axis of showers and
thunderstorms shifts south of the Mason-Dixon line. This is also the
window when the strongest upper forcing for large-scale ascent exits
the region, further supporting a brief decrease in heavy rain and
thunderstorm potential (especially north of I-70) during the day
Friday.

Yet another surface low is then expected to track NE out of the
Mississippi Valley region Friday night, pushing the front back north
this time as a warm front. Showers and thunderstorms once again
increase in coverage as the front and surface low move across the
Upper Ohio Valley region Friday night into early Saturday. Amounts
through the day on Saturday look to be highest from Pittsburgh and
north with forcing along the warm front and enhanced convergence on
the nose of an impinging 850 mb jet. We`ll briefly reside in the
warm sector before the cold front comes through in the latter half
of the day bringing yet another enhancement in rain coverage along
it. The severe weather potential should be limited due to weak
instability, however with repeated rounds of heavy rain and a
saturated ground, flooding potential will increase, especially with
rises on area rivers.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:

- Showers/thunderstorms with potential for heavy rainfall continue
  this weekend.
- A cold front moves through Sunday finally bringing an end to the
  heavy rainfall.
- Colder next week with lighter rain/snow chances each day.
-------------------------------------------------------------------

Showers and thunderstorms continue Saturday night as the surface low
tracks through the area, yet is still unable to effectively move the
stalled frontal boundary. Ensembles suggest another heavier period
of rain on the nose of another low level jet Saturday night into
Sunday morning falling on a then very saturated ground. However,
ensemble clusters all agree on a deep upper trough swinging across
the eastern CONUS on Sunday into Monday which will finally shunt the
surface ridge that had been firmly planted over the southeast CONUS
coast and allow a cold front to advance through the area and off to
the east bringing an end to the heavy rain and storm potential.
There`s some discrepancy in the timing of the upper pattern and how
quickly the trough axis arrives with the cluster dominated by the
GEPS suggesting a slower cessation of the rain in the Monday morning
hours.

The upper trough is then expected to persist across the NE CONUS
early next week, resulting in temperatures dipping to below normal
values and daily rain/snow chances, albeit not nearly as intense as
what we`re experiencing this week.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Residual showers and isolated thunderstorms ahead of an 850mb
warm front are expected to decay under the influence of broader
subsidence 2-3 hours after TAF issuance. VFR with 4-8kft
ceilings are expected through 06z within the warm sector of an
incoming low pressure system; development of a strong ~50kt
llvl jet is likely to remain above the inversion (and llws
height threshold) but enough sub-inversion mixing may foster SSE
gusts between 20-30kts.

A well-developed QLCS complex of showers/thunderstorms will
weaken as the enter the region after 06z, but uncertainty is
fairly high on initial intensity as it reaches ZZV and its
ability to maintain through western PA. TAFs noted that a likely
brief wind shift out of the west will occur with the line
before southerly synoptic winds prevail; thunderstorm intensity
will dictate if higher speeds can occur (more likely at ZZV and
trending down eastward).

Stagnation of the cold front driving the convective system is
likely somewhere near/south of KPIT, which may allow for a
brief period of MVFR cigs as moisture converges on the
stationary boundary. Brief dry weather and mixing will improve
cigs 12z-18z before additional shortwave movement aloft and any
trailing sfc boundary offers lower probability showers. Timing
of these showers and a more potent upper shortwave Thursday
night creates greater variability in precipitation timing and
restriction potential.

Outlook...
The Upper Ohio River Valley will remain positioned between a
Central Plains trough and Atlantic ridge that will foster
multiple rounds of moderate to locally heavy rain through Monday
morning. Timing and shape in each wave remains variable, which
may alter the axis of highest precipitation rates and areas of
greatest restrictions. Aviation customers should anticipate
limited windows of VFR and dry conditions through the period as
the pattern favors MVFR/IFR restrictions, heavier rain showers
and occasional thunderstorms.

A deepening upper trough may overtake the region early next
week, shifting towards a colder pattern featuring periodic
rain/snow chances and continued ceiling restrictions.

&&

.HYDROLOGY...
The potential for heavy rainfall will exist beginning tonight
and continuing into Sunday. At this time, areas across Ohio have
the potential to see the heaviest rainfall, where a Flood Watch
has been issued. Current NBM values indicate a 60 percent
chance or greater of at least 2 inches of rain over a 72 hr
period in this region. Lesser probabilities exist further east,
though a trend up has been noted in the latest ensemble guidance
and will need to be monitored for any potential expansion of the
flood watch. The exact location of the heaviest rain will
depend on the position of a quasi-stationary surface front.
Precipitable water is expected to remain elevated through
Sunday, with some periodic jet enhanced ascent. Even after the
heavy rain potential ends, river levels will likely remain
elevated for a few days. Current ensemble river forecast
projections also focus the most significant river rises across
Ohio.

Will monitor further trends for any future adjustments to the
watch.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...Flood Watch through Sunday morning for OHZ039-040-048-049-
     057>059-068-069.
WV...None.

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan/MLB
SHORT TERM...Cermak/MLB
LONG TERM...Cermak/MLB
AVIATION...Frazier
HYDROLOGY...WM/MLB